depending on the algal group The main difference is obviously the DNA content that is haploid instead of diploid Different combinations of gamete types are possible In the case of isogamy ID: 926541
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Slide1
SEXUAL REPRODUCTIONGametes may be morphologically identical with vegetative cells or markedly differ from them, depending on the algal group. The main difference is obviously the DNA content that is haploid instead of diploid.
Different combinations of gamete types are
possible,
In the case of
isogamy
, gametes
are both motile and indistinguishable.
Slide2When the two gametes differ in size, we have heterogamy.This combination occurs in two types:
anisogamy
, where both gametes are motile,
but one
is small (sperm) and the other is large (egg);
Oogamy
, where only one gamete is
motile (
sperm) and fuses with the other that is non-motile and very large (egg).
Slide3Algae exhibit three different life cycles with variation within different groups. The main difference is
the point where meiosis occurs and the type of cells it produces, and whether there is
more than
one free-living stage in the life cycle.
Slide4Haplontic or Zygotic Life CycleThis cycle is characterized by a single predominant haploid vegetative phase, with the meiosis taking place upon germination of the zygote.
Chlamydomonas
(
Chlorophyta
) exhibits this
type of life cycle
.
Slide5Slide6Diplontic or Gametic Life CycleThis cycle has a single predominant vegetative diploid phase, and the meiosis gives rise
to haploid
gametes. Diatoms
(A)
and
Fucus
(B)
have a
diplontic
cycle.
Slide7Slide8Life cycle of a diatom
Slide9Life cycle of Fucus sp
Slide10Diplohaplontic or Sporic Life CyclesThese cycles present an alternation of generation between two different phases consisting in
a haploid
gametophyte and a diploid sporophyte
.
The gametophyte produces gametes by mitosis
;
the
sporophyte produces spores through meiosis.
Slide11Alternation of generation in the algae can be isomorphic, in which the two phases are morphologically identical as in Ulva (Chlorophyta) (C) or heteromorphic, with the predominance of the sporophyte as in Laminaria
(
D)
or
with the predominance of the gametophyte as in
Porphyra
(
Rhodophyta
) (E).
Slide12Life cycle of Ulva sp
Slide13Life cycle of Laminaria sp.
Slide14Life cycle of Porphyra sp.
Slide15AnatomyCYTOMORPHOLOGY AND ULTRASTRUCTURE
The description of the algal cell will proceed from the outside structures to the inside components.
Details will be given only for those structures that are not comparable with analogue
structures found
in most animals and plants.
Slide16OUTSIDE THE CELLCell surface forms the border between the external word and the inside of the cell. It serves
a number
of basic functions, including species identification, uptake and excretion
/
secretion
of various
compounds, protection against desiccation, pathogens, and predators, cell signaling
and cell–cell
interaction.
Slide17It serves as an osmotic barrier, preventing free flow of material, and as a selective barrier for the specific transport of molecules.
Algae, besides naked membranes more typical
of animal
cells and cell walls similar to those of higher plant cells, possess a wide variety of cell surfaces.
Slide18The terminology used to describe cell surface structures of algae is sometimes confusing; to avoid this confusion, or at least to reduce it, we will adopt a terminology mainly based on that of Presig et al.
(1994).
Slide19Cell surface structures can be grouped into four different basic types:. Simple cell membrane (Type 1). Cell membrane with additional extracellular material (Type 2). Cell membrane with additional intracellular material in vesicles (Type 3)
. Cell membrane with additional intracellular and extracellular material (Type 4)
Slide20Type 1: Simple Cell MembraneThis cell surface consists of a simple or modified plasma membrane. The unit membrane is a lipid bilayer, 7–8 nm thick, rich of integral and peripheral proteins. Several domains exist in the membrane
, each
distinguished by its own molecular structure.
Slide21Some domains have characteristic carbohydrate coat enveloping the unit membrane. The carbohydrate side chains of the membrane glycolipids and glycoproteins form the carbohydrate coat. Difference in thickness of plasma
membrane may
reflect differences in the distribution of phospholipids, glycolipids, and glycoproteins
Slide22Slide23A simple plasma membrane is present in the zoospores and gametes of Chlorophyceae, Xanthophyceae , and Phaeophyceae
,
and in the spermatozoids of
Bacillariophyceae
This type of cell surface usually characterizes very short-lived stages and, in
this transitory
naked phase, the naked condition is usually rapidly
lost
Slide24The properties of the membrane or its domains may change from one stage in the life cycle to the next.